Optoelectronic packages generally include one or more optical dies, such as waveguide-based diode lasers, photo-detectors, and planar lightwave circuits (PLCs), enclosed in a cavity formed by a cap and a substrate to which the optical dies are attached. Optical signals from the optical dies are coupled to an optical fiber for communication over long distances. The optoelectronic packages generally rely on free space light propagation for transmitting the optical signals from the cavity for coupling with the optical fiber or an optical waveguide.
FIG. 1 shows a cross-sectional view of a first conventional optoelectronic package 100 for coupling optical signals to an optical fiber 102. In the first conventional optoelectronic package 100, an optical die 104 is attached to a sub-mount substrate 106, and a mirror 108 is fitted in a mirror guiding hole (not shown) formed on the sub-mount substrate 106. A cap 110, having a cavity 112, is attached to the sub-mount substrate 106 by way of a bond layer 114 therebetween. The bond layer 114 can be made from various materials, such as adhesive resins, solder material, and the like. The cap 110 includes a first lens 116 fitted in a lens guiding hole (not shown) that is formed on the cap 110. The mirror 108 receives a first optical signal OS1 that is parallel to the surface of the sub-mount substrate 106 from the optical die 104. The mirror 108 reflects the first optical signal OS1, thereby making the first optical signal OS1 perpendicular to the surface of the sub-mount substrate 106. After reflection, the first optical signal OS1 propagates in free space through the cavity 112 and the cap 110, and becomes incident upon the first lens 116. The first lens 116 focusses the first optical signal OS1 onto a second lens 118. The second lens 118 couples the first optical signal OS1 to the optical fiber 102, which in turn transmits the first optical signal OS1 over long distances to one or more remote devices (not shown).
FIG. 2 shows a cross-sectional view of a second conventional optoelectronic package 200 for coupling optical signals to an optical waveguide 202 of a silicon photonic chip 204. In the second conventional optoelectronic package 200, an optical die 206 is attached to a sub-mount substrate 208. A cap 210, having a cavity 212, is attached to the sub-mount substrate 208 by way of a bond layer 214 therebetween. The bond layer 214 can be made from various materials, such as adhesive resins, solder material, and the like. The optical die 206 emits a second optical signal OS2 in a direction that is parallel to the surface of the sub-mount substrate 208. The second optical signal OS2 becomes incident upon the internal surface of the cap 210, which is coated with a reflective material. The internal surface of the cap 210 reflects the second optical signal OS2. After reflection, the second optical signal OS2 propagates in free space through the sub-mount substrate 208, and becomes incident upon a third lens 216. The third lens 216 focusses the second optical signal OS2 onto a grating coupler 218, which is mounted on the optical waveguide 202. The grating coupler 218 couples the second optical signal OS2 to the optical waveguide 202, which in turn may couple the second optical signal OS2 to an optical fiber (not shown) for transmission to one or more remote devices.
In the first and second conventional optoelectronic packages 100 and 200, the first and second optical signals OS1 and OS2 undergo high propagation and reflection losses due to propagation in the free space, respectively. Further, the poor coupling efficiency of the second and third lenses 118 and 216 results in coupling losses of the first and second optical signals OS1 and OS2 into the optical fiber 102 and the grating coupler 218, respectively. A known solution for improving the coupling efficiency of the second and third lenses 118 and 216 is to use active alignment techniques for aligning the optical path of the second and third lenses 118 and 216 to the optical path of the optical fiber 102 and the grating coupler 218, respectively. However, the active alignment techniques are complex to implement. Further, the grating coupler 218 can couple optical signals that lie in a particular wavelength range to the optical waveguide 202. Thus, the grating coupler 218 limits the operational wavelength bandwidth of the second conventional optoelectronic package 200, which is undesirable.
In light of the foregoing, there exists a need for an optoelectronic package that prevents the propagation of optical signals in free space, has less propagation and reflection losses, large operation wavelength bandwidth as compared to the first and second conventional optoelectronic packages 100 and 200, and does not require additional components, such as lenses, for coupling the optical signals at its output.